1. Field of the Invention
The present invention relates to an acoustic transmission method and an apparatus for transmitting signals using sound waves as the transport medium.
This application is based on patent application Nos. Hei 11-329914, Hei 11-356827. Hei 11-363811, Hei 11-366345, Hei 11-366346, 2000-136716, 2000-136717, 2000-248800 filed in Japan, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Conventionally, when transmitting the sound that can be heard by humans or animals (audible sound signals) and associated information signals concurrently to some machine, the audible signal and the associated information signal are sent through separate channels.
For example, audible signal and information signal are sent as electrical signal to modulate the carrier wave, and are sent to the receiver side through electromagnetic waves and other media such as cables, and are used after demodulation by the receiver side. In such methods, it is necessary to provide respective transceivers for the purpose of sending an audible sound signal separately from another signal different than the audible sound signal.
That is, a total of more than two apparatuses are necessary, and complexity in the overall apparatus configuration is unavoidable. Also, apart from this problem, although there are methods of signal transmission based on ultrasonic waves as carrier waves, because ultrasonic sounds cannot be heard by human ears, it is necessary to convert to an audible sound at the receiver side, and the method cannot be used for the above purpose.
As a technology similar to the technologies described above for transmitting sound (audible sound signals) that can be heard by humans or animals simultaneously with associated information signals, is disclosed in a Japanese Unexamined Patent Application, First Publication, No. Hei 8-37511 “Interactive broadcasting system and receiving system”, Publication date, 6 Feb. 1996 (Reference 1), for example. This method is based on simply superimposing signals according to the DTMF (Dual Tone Multiple Frequency) format on the audible sound signals.
However, according to this method, sounds that are not needed to be heard and are not of any interest to humans can be heard clearly as background noise. Therefore, it is very disturbing, and possibilities exist of misunderstanding the intended meaning of the original sounds represented by the audible sound signals.
Therefore, such methods cannot be said to be suitable as sound-based information transfer means.